Heat transfer and friction factor characteristics in a double pipe heat exchanger fitted with variant twisted tapes

Abstract

Heat exchangers are widely used as essential units in heat extracting and recovering systems in industries. The performance of heat exchanger can be substantially improved by a number of augmentation techniques. The present work reported the use of variant twisted tapes fitted in a double pipe heat exchanger to improve the fluid mixing that leads to higher heat transfer rate with respect to that of the plain-twisted tape. Tests are performed for both laminar and turbulent flow Reynolds number ranges. The experimental data for a plain tube and plain-twisted tapes are validated using the standard correlations available in the literature. Seven different variant twisted tapes which include Trapezoidal cut-twisted tape, Square cut-twisted tape, U cut-twisted tape, V cut-twisted tape, Vertical wing cut-twisted tape, Horizontal wing cut-twisted tape and Wire nail-twisted tape with twist ratios of y = 2.0, 4.4 and 6.0 are used. Based on these studies, the following major conclusion has been arrived at; (i) The Nusselt number, friction factor and thermal enhancement factor of variant twisted tapes are higher than that of plaintwisted tape for the twist ratios of 2.0, 4.4 and 6.0 respectively. (ii) The variant twisted tapes heat transfer enhancement is better in the laminar flow than that of the turbulent flows. (iii) Among the variant twisted tapes used in the present work, the horizontal wing cut-twisted tape and wire nail-twisted tape give better performance in laminar and turbulent flow due to the effect of increased turbulence which improves the fluid mixing near the wall of the test tube. The predicted data for all the twisted tapes used in the present study are matching with the experimental data within the maximum deviation of ±12% for Nusselt number and ±10% for the friction factor respectively. Similarly, the simulated results are compared with experimental results of plain tube, plain-twisted tape and horizontal wing cuttwisted tape with the maximum deviation of ±13% for both Nusselt number and friction factor.